Why variable declaration fails in IF statemenet

[Guy1978]

As we all know, in Java you can combine an array declaration with array initialization, as follows:

n1 = 5;
double[] g = new double[n1 + 1];

But why is it that such a statement will not work if declared within the bounds of an IF statement? I had never heard before that variables cannot be declared within if statements! The code segment is as follows:

n1 = 5;
n2 = 7;
if (n1 > n2)
    double[] f = new double[n1 + 1];
else
    double[] f = new double[n2 + 1];

The code returns a compile error for both lines, saying:
".class expected" and "not a statement" for both of the array declarations/initializations. Could someone tell me why?
Thanks

 

[jstreich]

It does work... But the scope is the if statment.

if(codition)
{ 
  int i[200] = {...}; //i comes to exsist here
  i[1] += i[2];
} //ends exsistance here.
//i doesn't live here

Much like the scope of a try/catch, sychronize or function.
The way to do this is (with Objects, istead of primitives):

String s[];
if(condition)
 s = String[200];
else
 s = String[300];

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[Diancecht]

Just enclose it

int n1 = 5;
int n2 = 7;
if (n1 > n2) {
    double[] f = new double[n1 + 1];
} else {
    double[] f = new double[n2 + 1];
}

Cheers,

Dian

 

[Guy1978]

Hmmmm...what both of you said is interesting. I thought that the reference variable f would only be invisible outside the IF statement (and hence create a scope problem) if it were declared within braces. In fact, when I did as Dian suggested, the compiler no longer complained of ".class expected" or "Not a statement"; only later in the program, when f is passed as a parameter, did the compiler complain that f had not been declared (it was out of scope). So Dian's suggestion did make the ".class expected"/"not a statement" problem go away.

Jstreich, declaring the reference variable before the IF statement solved all the problems. But why did I get ".class expected"/"not a statement" for the variable declaration inside the IF statement. If it truly were a scope problem, would the compiler not have complained (at some other point in the program) that f had not been declared? Would I not have gotten the same compile error I got when I enclosed the variable declarations in braces?

Thanks

 

[idarke]

I think the IF statement requires some sort of executable expression after it. The variable declaration isn't considered an executable expression, hence your errors.

However, braces all by themselves ARE considered a valid expression. That's why you can just put {} after an if statement.

So, I don't think enclosing the declaration in braces made the error go away. I think just the existence of the braces did the trick - they fulfilled the requirement for an executable expression.